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Questions tagged [vigenere]

The Vigenère cipher is a classical cipher that shifts each plaintext character by the value of the key at the same position modulo the key-length.

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Creating your own encryption and decryption algorithm

I'm very uneducated when it comes to cryptography. I have tried to find an answer to my question, but what I've read doesn't quite cover what I'm asking. I have thought up my own encryption algorithm (which I'm sure is nothing new) and I would like…
user1575550
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How to solve cipher encrypted with Vigenère + Columnar Transposition?

Vigenère's weakness is Kasiski's test and index of coincidence. However, if you put columnar transposition on top of Vigenère, that weakness is gone. The text is now shuffled and you can't search for digrams/trigrams, because they will give you…
Pavancho Emiliano
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Finding a keylength in a repeating key XOR cipher

In an old cryptography FAQ, I found the following step described for determining a the length of the key a cipher was repeatedly XORed against: Discover the length of the key by counting coincidences. (See Gaines [GAI44], Sinkov [SIN66].) Trying…
hlh
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K Friedman - two texts explanation

I read the $K$-Friedman test to determine the period of a Vigenère ciphertext, and I understand something like this: $K$-Friedman test tries to find out what period of the cipher by calculating some values of $K(C,C^n)n$, where $C^n$ is the…
PRVS
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Why is Vigenère Autokey self-synchronizing?

According to the Wikipedia, and to several of our school study materials, Vigenère autokey ciphers are considered to be self-synchronizing stream ciphers. If I understand it correctly, the main idea of self-synchronizing ciphers is that they should…
Mikuláš Hrdlička
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Affine Cipher over an Affine Cipher

I would like to know your view about the title, encrypting a plain text with an affine cipher then encrypting that ciphertext once more using the same cipher, but of course different keys. Would it be more secure? For me, it won't be since it still…
rockStar
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How can a Vigenère cipher be broken if the message is short?

I was watching a Stanford lecture on Vigenère cipher and in it the professor said that – to break the cipher – we assume the length of the key is known. We then break the cipher into groups of this known length and then pick up (successively) the…
user3676846
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Solving Vigenère Encryption

I'm trying to crack a cypher that I believe is Vigenère encrypted and I'm currently stuck. I calculated the key length by finding repeated sequences in the cypher and calculating the the common factors. Word distance factors agzd 16 …
vignere_solve
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Is there an English translation of Vigenère's "Traicté des Chiffres"?

I Googled Vigenère's "Traicté des Chiffres": no English translations, not even a reference to one. Perhaps someone's Google-wu is better than mine; I can't find it. I'm slogging my way through a PDF of the 1586 edition of "Traicté Des Chiffres, ou…
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When does a multiple Vigenère cipher become intractable?

Multiple Vigenère ciphers do not repeat the key until the message gets longer than the LCM of the cipher lengths. Are messages shorter than that safe? If not, what is the attack strategy? I believe there is a known plaintext attack which has an…
Jim Rootham
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Conditions for Perfect Secrecy with the Vigenere Cipher

Please forgive my ignorance here as I'm far from a math major and I've never looked into cryptography before so if this seems stupid - it probably is. There is a question in a quiz I'm attempting that is just doing my head in. If you are wondering -…
Chris
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Relative security of a Vigenère cipher

Within a closed computer network, I am ciphering some plaintext data as an added security measure. This is below several other layers of protection. For various technical reasons, I am restricted to plain-text, UTF-8 data. To that end, I have been…
Chris
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What is the difference between a Vigenère cipher and a one time pad cipher?

I'm doing a decryption competition at a nearby college. We are allowed one cheat sheet so I'm trying to make one. I realized that the Vigenère cipher was very similar to the one time pad and wanted to make sure that I know the difference. As I…
StandingFuture
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Can I make a cipher (ex: Vigenère) harder to break?

The Vigenère cipher can relatively easy be broken when the key size is small compared to the size of the message. One first finds the length of the key, and then uses frequency analysis to actually find the key. How can one "add" something…
Thomas
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A "one time pad" can be thought of a Vigenere cipher with

A "One Time Pad" can be thought of a Vigenere cipher with... An infinitely long key A secure symmetric key Multiple ciphertext alphabets A columnar transposition I had this question come up today in one of my mid-terms and to be honest it…
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